1. Field of the Invention
This invention relates to a power drive unit, more specifically to a power drive unit that is most suitable for use in a hybrid vehicle.
2. Description of the Related Art
The hybrid vehicle that has emerged in various forms in recent years is equipped with an internal combustion engine, electric motor(s), battery or other such energy storage device, and the like. During driving of the hybrid vehicle, the engine and motor(s) are controlled in response to the driving or running conditions of the vehicle (e.g., whether the vehicle drives at high speed or low speed).
The electric motor used in a hybrid vehicle is generally operated by alternating current supplied to its stator from a power drive unit (PDU), more exactly from power modules in the PDU that convert direct current (outputted from a battery or other energy storage device) into alternating current.
In the PDU, alternating currents flowing through bus bars (i.e., bar-like leads) extending from the power modules (specifically, three-phase inverter circuit modules) are detected by current sensors (current detectors) that output signals proportional to the detected alternating currents to a control circuit board (more specifically a control unit mounted on a circuit board). The control unit on the circuit board controls the PDU based on the signals outputted from the current sensors.
In order to reduce the size of the PDU, the distance between the control circuit board and current sensors should preferably be made as small as possible. A widely employed expedient for achieving this is to connect the control circuit board and current sensors through a harness, as taught, for example, in Japanese Laid-Open Patent Application No. Hei 9(1997)-47034, especially FIGS. 1 and 4. However, the PDU of this prior art with a harness disadvantageously increases both the number of components and the number of assembly steps.
This disadvantage can conceivably be overcome by interconnecting the control circuit board and the current sensors through lead pins. In this case, consideration must be given to the harsh environment of the PDU installation site, namely the severe vibration and temperature changes that the PDU experiences.
To cope with this situation, Japanese Laid-Open Patent Application No. Hei 11(1999)-26955 (especially paragraphs 0016 and 0017 and FIG. 1) teaches the control circuit board connected to external devices through lead pins, in which the stress produced in the lead pins can be alleviated by forming a convex curved portion in the vicinity of the intermediate region of the lead pins.
However, when the configuration taught by the second reference ('955) is applied to the PDU, the distance between the control circuit board and current sensors needs to be increased by the size of the curved portion of the lead pins, which is disadvantageous because it makes the overall size of the PDU larger by the amount of the increased clearance.